The PIM protein kinase family which consists of the closely related PIM-1, 2, and 3, have been implicated in diverse biological processes such as cell survival, proliferation, and differentiation. PIM-1 is involved in a number of signaling pathways that are highly relevant to tumorigenesis [reviewed in Bachmann & Moroy, Internat. J. Biochem. Cell Biol., 37, 726-730 (2005)]. Many of these are involved in cell cycle progression and apoptosis. It has been shown that PIM-1 acts as an anti-apoptotic factor via inactivation of the pro-apoptotic factor Bad. This finding suggested a direct role of PIM-1 in preventing cell death since the inactivation of Bad can enhance Bcl-2 activity and thereby promotes cell survival [Aho et al., FEBS Letters, 571, 43-49 (2004)]. PIM-1 has also been recognized as a positive regulator of cell cycle progression. PIM-1 binds and phosphorylates CDC25A, which leads to an increase in its phosphatase activity and promotion of G1/S transition [reviewed in Losman et al., JBC, 278, 4800-4805 (1999)]. In addition, the cyclin kinase inhibitor p21Waf which inhibits G1/S progression was found to be inactivated by PIM-1 [Wang et al., Biochim. Biophys. Act. 1593, 45-55 (2002)]. Furthermore, by means of phosphorylation, Pim-1 inactivates C-TAK1 and activates Cdc25C which results in acceleration of G2/M transition [Bachman et al., JBC, 279, 48319-48 (2004)].
PIM-1 appears to be an essential player in hematopoetic proliferation. Kinase active PIM-1 is required for the gp130-mediated STAT3 proliferation signal [Hirano et al., Oncogene 19, 2548-2556, (2000)]
PIM-1 is overexpressed or even mutated in a number of tumors and different types of tumor cell lines and leads to genomic instability. Examples for a possible involvement of PIM-1 in human tumors are prostate cancer, oral cancer, and Burkitt lymphoma (Gaidano & Dalla Faver, 1993). All these findings point to an important role of PIM-1 in the initiation and progression of human cancer, and it appears that small molecule inhibition of PIM-1 activity is a promising therapeutic strategy. Finally, PIM-2 and PIM-3 have overlapping functions with PIM-1 and inhibition of more than one isoform may provide additional therapeutic benefits.
Accordingly, the identification of compounds that specifically inhibit, regulate and/or modulate the signal transduction of PIM, is desirable as a means to treat or prevent disease states associated with abnormal cell proliferation, such as cancer.